1. Field of the Invention
The present invention relates to a power semiconductor device made up of multiple kinds of semiconductor switching elements, for an example an insulated-gate bipolar transistor (IGBT) and a metal oxide semiconductor field effect transistor (MOSFET), with differing turn on/turn off operation characteristics being provided in parallel, and in particular, relates to a semiconductor switching device with a simple configuration such that surge or switching loss occurring when the multiple kinds of semiconductor switching elements are turned on and off can be reduced.
2. Description of the Background Art
A switching power supply device such as a DC-DC converter or a power conversion device, such as an inverter, that drives a motor is made up of a power semiconductor element such as an IGBT or MOSFET as a semiconductor switching element for switching input power. Also, with regard to this kind of semiconductor switching device, there is strong demand for surge or switching loss occurring when the power semiconductor element is turned on and off to be reduced.
To date, in order to satisfy this kind of demand, using an IGBT, which has barrier layer voltage and in which voltage drop in a large current region is small, and a MOSFET, which has a constant resistance characteristic, in parallel has been proposed as the power semiconductor element.
The barrier layer voltage refers to voltage that does not cause current to flow in a low voltage region C, as shown in IGBT voltage-current characteristic A in FIG. 7. Also, the constant resistance characteristic is a characteristic that causes current in accordance with the on-state resistance of a semiconductor element (such as a MOSFET) to flow from when a voltage VDS applied to the MOSFET is zero until the voltage VDS becomes a predetermined voltage, as shown in MOSFET voltage-current characteristic B in FIG. 7.
A semiconductor switching device configured using the IGBT and MOSFET in parallel may be configured so that input power is turned on and off (input power is switched) utilizing the constant resistance characteristic of the MOSFET in a low current region and utilizing mainly the low voltage drop characteristic of the IGBT in a high current region. According to the semiconductor switching device with this kind of configuration, low-loss switching is realized with respect to changes in load powers of low currents to high currents, whereby more efficient power conversion can be achieved. That is, the semiconductor switching device with the heretofore described configuration is such that switching loss in the IGBT, which has a long turn-off time, is reduced by controlling timing so that the MOSFET is turned on prior to the timing at which the IGBT is turned off.
JP-A-4-354156 describes providing a difference between the resistance values of gate resistors provided between the gate of each of an IGBT and a MOSFET provided in parallel and an output terminal. Also, JP-A-2002-165439 describes technology whereby switching loss is reduced by an IGBT and MOSFET provided in parallel as switching elements being such that the turn-on timing of the IGBT is shifted so as to be later than the turn-on timing of the MOSFET when the switching elements are turned on, and the turn-off timing of the MOSFET is shifted so as to be later than the turn-off timing of the IGBT when the switching elements are turned off.
Specifically, when applying the technology disclosed in either JP-A-4-354156 or JP-A-2002-165439, the resistance value of a gate resistor corresponding to a MOSFET can be greater than the resistance value of the gate resistor corresponding to the IGBT.
According to a circuit that provides a difference between the resistance values of the gate resistors in this way, the turn-on timings and turn-off timings of the IGBT and MOSFET can be adjusted. Specifically, the MOSFET can be turned off after the IGBT is first turned off by the first gate drive voltage output from a driver circuit.
Conversely, the IGBT can be turned on after the MOSFET is turned on by the second gate drive voltage output from the driver circuit by the resistance value of the gate resistor corresponding to the MOSFET being smaller than the resistance value of the gate resistor corresponding to the IGBT. As a result of this, switching loss when the switch made up of the IGBT and MOSFET is turned on can be reduced.
However, in the examples described above, switching loss can only be reduced either when the semiconductor switching elements are turned on or when the semiconductor switching elements are turned off, and switching loss cannot be reduced both when the semiconductor switching elements are turned on and when the semiconductor switching elements are turned off.
Alternatively, resistors of resistance values smaller than those of the gate resistors may be provided in parallel to the gate resistors respectively via diodes. The configuration can also be such that the resistors with the smaller gate resistance act via the diodes only when the switch is turned on or only when the switch is turned off.
According to a circuit configured in this way, the first gate drive voltage output from the driver circuit may be applied promptly to the gate of the MOSFET via a resistor with the smaller resistance value, after which the first gate drive voltage output can be applied to the gate of the IGBT via a gate resistor with a greater resistance value. Also, the second gate drive voltage output from the driver circuit may be applied promptly to the gate of the IGBT via a resistor with a smaller resistance value, after which the second gate drive voltage output can be applied to the gate of the MOSFET via a gate resistor with the greater resistance value.
In this case, however, there are two resistors and two extra diodes, because of which the circuit configuration is relatively complex, and the manufacturing cost increases.
In another example, two driver circuits may be provided in parallel corresponding to the IGBT and MOSFET respectively. However, in such a configuration, the circuit configuration is complex and the manufacturing cost increases.